So this is completely random, but I thought I would throw it out to you peeps since you are a savvy bunch. I recently got a new late 2013 Haswell iMac and have been experiencing some erratic USB issues. I managed to solve some issues by removing a USB hub that was causing all USB devices to fail, but I am still getting an issue where I get pops and glitches on my ODAC and when recording with my Zoom H1 recorder.
Doing some hunting around, it seems that some people have issues with USB 3.0 and audio interface devices. It didn't even occur to me that this might be the cause of the problem since I thought that USB 3.0 was fully backwards compatible. I found two threads:https://discussions.apple.com/thread/4980646?start=0&tstart=0 and http://www.head-fi.org/t/599915/issues-with-usb-3-0
Any of you have USB 3.0 ports on your computers that are causing you any grief?
EDIT: Here is something really interesting I found in this thread: http://forums.presonus.com/posts/list/33427.page
Apparently Intel USB 3.0 chipsets do not have compatibility with the USB isochronous streaming protocol.
My iMac has a Intel USB chipset, which I can identify from the device vendor ID in system report. The ODAC apparently uses isochronous transfer mode. This may be the cause of any glitches. If this is so, this is something really frustrating because it is virtually inescapable for me...
I'm no techie but a friend of mine was having troubles with USB 3 on his Mac and he solved it with a good USB hub. I don't know, you're a part of Cymbacavum. Maybe THIS might solve your problems? Tom seems to really be impressed by it. Try asking Coq De Combat, he's a techie who could probably recommend a fix to try.